The U.S. Air Force has successfully tested an experimental aircraft called the X-51A Waverider. This unmanned vehicle traveled at Mach 6 (six times the speed of sound) for 200 seconds, crushing the 12 second flight record of earlier models.
The X-51A, built by Boeing with a Pratt & Whitney Rocketdyne engine, is a supersonic version of a ramjet. This type of craft is therefore dubbed a ‘scramjet’. Unlike conventional jets, which use fans to compress air in the engine prior to igniting it, ramjets use the aircraft’s speed to compress the incoming air. Ramjets have to slow the incoming air to subsonic levels, whereas scramjets use supersonic airflow through their engines.
Obviously, this was only a preliminary test with an unmanned vehicle. However, to put this kind of speed into perspective, if an equivalent manned scramjet could safely fly for an extended period, it could take its passengers from New York to London in about three quarters of an hour.
According to Charlie Brink, a X-51A program manager with the Air Force Research Laboratory at Wright-Patterson Air Force Base:
We equate this leap in engine technology as equivalent to the post-World War II jump from propeller-driven aircraft to jet engines.
The X-43 is the previous model of scramjet.